Display panels are usually designed to support a sequence of rapidly changing images which the user sees as motion video. In some applications the image displayed is static for long periods of time. Traditionally this is accomplished by sending the same image repeatedly to the display. Continuous refresh means that the source device, such as a graphics processor chip for example, must be continuously powered and consuming energy.
Many arrangements are possible for display panels. FIG. 1 shows a conventional liquid crystal display (LCD) panel 10 and associated circuit arrangement. The display panel has a timing controller (T-Con) 20 that receives differential signals such as low voltage differential signaling (LVDS) or any other suitable signaling at 25 as received from a video source such as a graphics chip 28. The T-Con is often considered a part of the display panel assembly 10 and will be treated as such throughout this document, but it will be understood that the T-Con may in fact be realized in a separate circuit assembly that is not physically attached to the panel. Output signals are provided in a matrix arrangement to a plurality of drivers 32 and 36 shown as horizontal drivers and vertical drivers respectively for driving pixels of the display panel 42. A particular pixel can be selected to be driven to a particular brightness (or transmissivity). By addressing the pixel according to its horizontal and vertical location in the panel and applying a suitable signal thereto. Conventionally multiple such pixels (e.g., three or six) are illuminated simultaneously to produce a point in an image having a particular color, and brightness characteristics. Such points in an image are commonly also called “pixels”, but for purposes of this document, the term will generally be used to reference any of the single pixels used to form a point in an image. Other panel arrangements are also possible, and embodiments consistent with the present invention are equally applicable to such arrangements.
LCD Display panels such as 42 are inherently inefficient in transmission of light. The LCD's control circuitry (T-Con 20 in conjunction with H-driver 32 and V-diver 36) is used to control the transmissivity of the LCD pixels so that light produced by a backlighting light source is controlled in color intensity. However, the amount of light that passes through the pixel is limited to around 3-5% of the light intensity of the backlight. Transistors and other circuit elements are often fabricated on the LCD panel itself adjacent the pixel, e.g., the pixel's driving transistors and voltage holding capacitor. However, any such circuitry including light sensitive elements is coated with light impervious material to eliminate or reduce photoelectric responses of those devices themselves. Thus, such circuitry appearing directly on the LCD panel itself is preferably minimized since its presence further reduces the efficiency of light transmissivity and furthermore affects the density of pixels that can be displayed on a given panel.